Cylinder-piston combination, particularly for high-pressure application

ABSTRACT

A deformable sealing member, particularly a sealing tube, which is at least partially elastic is secured at two distant locations to two working members, e.g. to a piston part and a cylinder part respectively to form a leakproof working chamber for pressurizing therein a working fluid or for transferring the power of a pressurized working fluid introduced in the working chamber to said working members, the apparatus thus being able to operate as a pump or motor respectively. The sealing member is supported against the working pressure in said chamber by a support surface, and between said sealing member and said support surface there being a low-friction component which is constituted by a solid material, e.g. a sliding layer, secured to the sealing member or to the support surface, or by a fluid lubricant introduced in a flow passage formed between the sealing member and the support surface, in the latter case there being a continuous or intermittent stream of lubricant through this lubricant flow passage at least during high-pressure strokes of the working chamber to a low-pressure side. The pressure in the lubricant flow passage is balanced against the pressure of the working fluid by throttle means formed by the gap between the deformed sealing member, when under pressure of the working fluid, and the support surface and automatically adjusted or regulated by the lubricant volume or pressure in said passage on one side and by the working pressure in said chamber on the other side so that substantial pressure balance between both surfaces of the sealing member wall will arise supporting the sealing member with distance from the support surface, i.e. substantially without friction and wear, and without excessive deformation. If solid low friction layers or surfaces are used, then &#34;Teflon&#34; or similar materials may be disposed on the sealing member and/or the support surface.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of my U.S. application Ser.No. 127,590, filed Mar. 6, 1980 now U.S. Pat. No. 4,329,914 which, inturn, is a continuation of my U.S. application Ser. No. 860,183, filedDec. 13, 1977, now abandoned, which, in turn, is a continuation of myU.S. application Ser. No. 639,700, filed Dec. 11, 1975, thelast-mentioned application having since become abandoned.

Further reference is made to Swiss patent application No. 3262/79 in thename of Hydrowatt Systems Ltd., London, filed Apr. 6, 1979, concerningthe introduction of lubricant in low-pressure strokes.

BACKGROUND OF THE INVENTION

The present invention relates to a piston and cylinder combination andmore particularly to a piston-cylinder structural arrangement forhigh-pressure, hydraulic pumps or motors, including motor devices forcontrol positioning of heavy loads, remote control positioning, remotecontrol locating, servo positioning, and the like. Combination of dualpiston-cylinder arrangements can provide push-pull or double-actingeffects.

Specifically, the present invention is directed to the structuralarrangement which provides for tight closure of the fluid, preferablyhydraulic fluid within a working chamber, e.g. a cylindrical chamber ofvariable volume as defined by the position of a piston as one workingmember being disposed in a cylinder as the other working member. Suchclosure is effected by means of a deformable sealing member, preferablya flexible elastic sealing tube, preferably made of an elastomer whichis attached at two locations having distance from each other, e.g. withits respective ends, to the working members, e.g. piston and cylinder,respectively to form a leakproof, sealed, tight connection for theclosure of working fluid which may be under very high pressure, forexample in the order of 100 at gauge.

Piston-cylinder arrangements for high pressure application provided withleakproof seals are difficult to use in continuous high-powerapplications in which high operating frequencies, high operating speedsand high pressure arise. The low mechanical strength of the sealingtubes has heretofore inhibited such applications because, to provide aleakproof, tight seal, the sealing tube must be secured to the workingmembers which move relatively to each other so that the sealing membermust undergo frequently repeated deformations under heavy forcespressing a surface of the member against a support surface in relationto which the member is partially moved. Therefore, high frictionalforces arise which can be reduced only by special arrangements. Heat dueto friction as well as the frictional force itself cause rapiddeterioration of the elastic portions of the seal; typically ofelastomer material. Moreover the sealing member generally has heretobeen locally clamped and has been terminated by an abrupt transition onthe respective support element, that is, the piston or the cylinderdisposed at the end of the tube under consideration. These terminationsresulted in high-stress gradients in radial direction at localizedpoints or zones of the sealing tube. These high stresses greatly reducedthe durability of the sealing tubes.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a piston-cylindercombination forming an apparatus which is so constructed that it permitshigh power or force transfer by means of fluid media with highefficiency and at high speed in continuous operation, without losing itsleakproof seal of the fluid working medium.

Briefly a deformable sealing member, e.g. an elastically deformable tubeis provided which is slidable with respect to one working member. Thesealing member preferably a sealing tube, is supported on a supportsurface through a solid or fluid low-friction component. The supportsurface typically is secured to or formed by the one of the workingmembers in relation to which the sealing member is disposed in slidingconnection.

The solid low-friction component may include a solid sliding coating orlayer cover on the support surface for the sealing tube. The solidlow-friction component may also be disposed on the sealing tube and thenis extendible or stretchable and bonded or is secured or is part of thesurface thereof. The low-friction component may also be a fluidlubricant introduced between the sealing member or sealing tube and thesupport surface so that the lubricant under the action of the workingpressure applied to the wall of the sealing member by the medium in theworking chamber flows through and out of the gap between the supportsurface and the surface of the sealing member facing this supportsurface (in the following text shortly named the "facing surface" of thesealing member) to a low-pressure side. Thereby the support surface isprovided with a fluid flow bearing which acts like a hydrodynamicbearing, i.e. by means of the hydrostatic pressure component in theflowing lubricant. The lubricant flow is conducted through a throttlemeans or choke to the low-pressure side. The choke preferably is formedby a gap between the sealing tube and the support surface. The chokemaintains the pressure balance between the lubricant and the workingmedium before the lubricant can be relieved of pressure and escape,preferably for recycling and re-use. The choke or throttle means may beformed by a portion of the sealing member, the surface of which is soconstructed that in unloaded or unstressed condition it has some radialdistance from the support surface; upon loading, a choke-type gap ofreduced width compared with said distance in the unloaded or unstressedcondition is formed, the size of which depends on the pressure of theworking medium as well as the pressure of the lubricant or the lubricantvolume present in the gap between the sealing member and the supportsurface so that the width of the gap will be self-adjusting in the senseof an automatic regulation or control of the lubricant pressure in thegap between the sealing member and the support surface so as tosubstantially balance the working medium pressure. The lubricant may bebranched off from the working pressure fluid if this fluid is a liquidwith lubricating properties. The deformable sealing member, preferably atube-like element made of elastic material like a suitable elastomer,may be secured to the one of the working members which moves relativelyto the support surface, in the region of a specifically shapedtransition zone the wall-thickness of which varies in the direction fromthe working chamber to the low-pressure side in such a manner that thepressure exerted by the sealing member on the support surface via thelow-friction component decreases in the said direction. In other words,the transition zone is arranged so as to transmit a portion of saidworking fluid pressure to the lubricant fluid and thereby to saidsupport surface. The transmitted portion of the working fluid pressuredecreases downstream with the flow of lubricant fluid along thetransition zone towards said lubricant fluid outlet, the non-transmittedportion of the working fluid pressure being at least partiallytransferred via said connection interface to said movable workingmember. Further, the sealing member has preferably a wall-thicknesswhich decreases over at least part of the length of said transition zonein the said direction from the working chamber to the low-pressure side,which kind of shape has proven to most conveniently establish saiddecreasing support pressure and leads to reduced stress concentrationsin the transition zone. Thus the decreasing wall-thickness in thetransition zone preferably in combination with a portion of enlargedwall-thickness at the end of the transition zone located near theworking chamber, i.e. of enlarged wall-thickness when compared with theone in the region of the sealing member extending over the workingchamber has proven to be the "best mode of operation".

The transition zone is preferably formed of a plurality of partialelements, particularly at least two parts which are constructed ofmaterials of different stiffness or resistance to deformation. This is afurther measure which can be taken in order to establish a convenientpressure profile in the transition zone. The partial elements in thetransition zone can be arranged in various ways; it is preferred,however, that at least one of the elements of lower stiffness thananother, or others, forms at least a portion of the surface of thetransition zone. The transition zone is usually loaded by the workingmedium at working fluid pressure and thus forms the throttle meansexplained above in the case of a lubricant fluid flow between thesealing member and the support surface being the low-friction component.A deformation in the transition zone results in a width of the throttlegap which depends on the pressure of the working medium and the pressureof the lubricant or the volume present in the gap of lubricant flowpassage between the sealing member and the support surface in the regionof the transition zone, this deformation establishing theself-adjustment or automatic regulation of the throttle means in thesense of maintaining the balance between the working and lubricantpressure. The deformation depending, in general, on the particular shapeand stiffness of the different elements as well as on the shape of thejunction surfaces between the various elements.

For reliable transfer of the stress under operating conditions betweenthe sealing member and the adjacent working member it is preferable toestablish a chemically or physically bonded junction between thetransition zone and the working member as well as between the separatepartial elements of the transition zone.

In a preferred form, the lubricant for supporting the sealing member isintroduced in said gap or passage with a volume flow rate which isindependent of the lubricant pressure in said gap or passage. This tendsto secure the sealing member against damage by excessive deformation incase of said self-adjustment or regulation failing to operate as well aswhen introducing the lubricant in a low-pressure interval of theoperating cycle.

On the other hand it is in many cases preferable to limit the intervalsof introducing the lubricant in the gap or passage partially orcompletely to low-pressure strokes in the course of the operating cyclesin case such low-pressure strokes occur in the prevailing mode ofoperation. This mode of lubricant introduction makes it possible to uselow injection pressures which allows for comparatively simple andinexpensive lubricant injection pumping devices.

As a matter of course, in such a low-pressure interval enough lubricanthas to be introduced in the gap or passage so as to establish sufficientreserve for maintaining lubricant flow through the passage and thethrottle means to the low-pressure side necessary for the pressurebalance on both sides of the sealing member wall. Suitable non-returnvalving means in the lubricant feed line has to be installed in order tomaintain the pressure in the lubricant flow passage during the followinghigh-pressure stroke.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be better understood and objects other than those setforth above, will become apparent when consideration is given to thefollowing detailed description thereof. Such description makes referenceto the annexed drawings wherein:

FIG. 1 is a longitudinal sectional view of a piston-cylinder apparatusin which a resilient sealing tube is loaded internally by the workingfluid;

FIG. 2 is a transverse section along line II--II, with the interiorelements of the arrangements omitted:

FIG. 3 is an enlarged fragmentary view of the region circled in FIG. 1and identified at III;

FIG. 4 is a longitudinal sectional schematic view of a piston-cylinderarrangement in which the working pressure fluid is applied to theoutside of the sealing tube;

FIG. 5 is a fragmentary cross-sectional area of one form of the sealingtube at the fixed non-movable end thereof;

FIG. 6 is a fragmentary transverse section of a portion of thecylinder-piston arrangement illustrating a portion of the piston and thetransition zone of the sealing tube with two elements;

FIG. 7 is a view similar to FIG. 6, having a transition zone with threeelements;

FIG. 8 is a transverse section similar to FIG. 6, showing a transitionzone having four partial elements with junction surfaces below the topsurface of the transition zone;

FIG. 9 is a transverse section of a transition zone having six partialelements;

FIGS. 10 and 11 are transverse sections of a transition zone havingseven partial elements;

FIG. 12 is a fragmentary sectional view of a transition zone havingthree partial elements joined to an elastic, flexible metal tube; and

FIG. 13 is a transverse sectional view of a transition zone having twopartial elements.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The cylinder-piston combination (see FIG. 1) has a cylinder element 1,of approximately square or rectangular outer cross section (see FIG. 2)with a bore 2. The cylinder is closed off at one end by a cylinder endcover 3 secured thereto, for example by means of bolts (not shown), andforms a working chamber. The junction surface between the cylinder body1 itself and the cover 3 is sealed by an O-ring 5 located in a groove 4of the cylinder 1. A piston 6, which is essentially cylindrical orslightly conical and which forms the other working member, is located inbore 2 and guided therein by means of a piston rod 7. The piston rod 7is slidable in a sleeve 8 which, in turn, is secured to a holder orclamp 9. The holder 9 extends through a bore 10 formed in the cover 3 ofthe cylinder and is secured therein by means of a nut 11. The holder 9is formed with a longitudinal duct 12, extending lengthwise thereof,terminating in mouths or openings 13 at the inside and in a pipecoupling at the outside. The pressure working medium which may, forexample, be a pressurized gas, hydraulic fluid or the like, isintroduced or removed from the interior of the cylinder through the duct12 and the openings 13 thereof. The holder 9 is formed with a thickenedregion 14 in the vicinity of the mouths 13. The thickened region 14 hasridges thereon. The thickened region 14 is used to clamp the fixed end16 of an elastic sealing tube 17 between the inner wall of the bore 2 ofthe cylinder and the outer surface of the holder 9. The tube 17 isclamped tightly between thickened region 14 and the inner wall of bore 2to form in its interior a leakproof working chamber. The other end 18 oftube 17 is connected through a transition zone A to the piston 6. Thetube 17 within the transition zone A is formed of two partial elements60, 70, secured together at junction surface 62. The partial elements60, 70 have different stiffness; the partial element 60 may be made ofthe same material as the sealing tube 17 and has a lower stiffness thanthe partial element 70 which merges into the piston 6 and may form aperipheral region thereof.

Operation: when pressure fluid is admitted through connection 11 andduct 12, the piston 6 will be forced to the right (FIG. 1) and tube 17will elongate, and hence deform. The partial element 70 has a greaterstiffness than partial element 60. The attachment at the junctionsurface may be by means of a physical adhesive or chemical bonding. Atthe side of the working chamber a thickened region 61 is provided in thetransition zone A to influence the deformation of this zone and,further, to increase the junction surface 62.

The outside of the sealing tube 17 has a layer forming a durable slidingor low-friction surface 21 applied thereto. Surface 21, which may be inform of a thin layer, is securely adhered to the tube 17. It isimportant that the surfaces between the tube 17 and the inner wall ofthe cylinder 1 be of low friction; thus, the sliding surface may also beapplied to the interior wall of the cylinder 1, and, if desired, slidinglow-friction surface layers can be applied to both the tube 17 and theinner wall of the bore 2 of the cylinder 1. The outer dimension of tube17 at zone A is such that a slight gap permitting radial play will beleft between it and the wall of cylinder 1.

A ring groove 19 is located at the transition or junction between thecylinder 1 and the cover 3 (FIG. 3). The groove 19 is connected by meansof a passage 20 with the bore 2 of the cylinder. The groove 19communicates with a duct 22 (FIG. 2) formed in the wall of thecylinder 1. Duct 22 is in communication with a connecting line 23 whichis connected to the cylinder 1 by means of a pipe thread coupling. Astream of pressurized lubricant is applied through duct 23, preferablyindependent of the working fluid pressure. The lubricant passes throughthe groove 19 into the gap or passage 20 between the outside of thesealing tube 17 and the inside wall of the bore 2 of the cylinder, whichwall forms a support surface for the tube. It will spread at the outercircumference of the sealing tube 17 and can escape from between tubeand support surface at the piston end of the cylinder-pistoncombination. The axial and particularly the radial deformation of thewall of the tube 17 in the transition zone A depends on the pressure ofthe working fluid and on the pressure of the lubricant stream or thelubricant volume in the gap or lubricant flow passage between the tubeand the support surface within the transition zone and upstream thereof.The radial deformation of the tube wall, by which the "facing surface"of the tube gets closer to the support surface, typically increasesunder the combined action of the pressure in the lubricant flow passageand the drop thereof near the low-pressure side as well as of theworking fluid pressure from the upstream end of the transition zone inthe lubricant flow direction to a maximum and then decreases over theremaining length of the transition zone to the location of escape of thelubricant at the low-pressure side. Therefore, at the location of thesaid maximum radial deformation, i.e. of the minimum distance betweenthe "facing surface" and the support surface, the gap or lubricant flowpassage has its minimum width. Due to this deformation effect, in thisregion a self-adjusting or automatically regulated throttle acting as ahydraulic choke with respect to the lubricant at the outside of tube 17is formed, which throttle or choke will achieve a pressure balance withthe pressure of the working fluid or medium within tube 17, and activeon piston 6. As far as the sealing tube 17 is concerned, therefore, theforces acting thereon will be in balance without physical contact,friction and wear between the tube and the support surface. Thus thesealing tube, the inside of which is loaded by the pressure of theworking fluid, is supported at its outer circumference or "facingsurface" by a thin flowing film of lubricant in pressure-balance withthe pressure of the working fluid. Thus, the sealing tube is supportedby the inner wall of the bore 2 of the cylinder without, however,touching the wall of the cylinder, so that the tube can slide freelywith respect thereto. Tube 17 is supported thus by a hydrostatic-likebearing. The resulting friction is extremely low.

The lubricant which escapes at the piston-end of the combination iscollected and re-cycled. A collecting bellows 25 is located at thepiston-end of the cylinder 1. Bellows 25 is secured in the groove 26 andmay be held at the outside by a clamp ring, if needed. The bellows isnot stressed by fluid pressures and thus no specially devised orconstructed holding arrangement is needed. The bellows 25 is centrallysecured to piston 6 by means of a bolt 27 and clamped between a cover 28and an internal shield 29. Shield 29 itself is held by a sleeve 30supported on a shoulder 31 formed in the piston 6.

The lubricant collected within the bellows 25 is removed by means ofducts 32, 33 (FIG. 2) formed in the cylinder 1 and connected to aremoval line 34. The ducts 32, 33 can be arranged in any suitableconfiguration and it is only necessary to so locate them that lubricantcan be removed from the bellows 25. They may for example, be secured influid-tight connection through a small opening formed in the bellows 25itself and, since the fluid therefrom will not be under pressure, can beremoved by a flexible, for example, plastic tubing.

FIG. 4 illustrates an arrangement in which the sealing tube 35 is loadedby pressure fluid at the outside thereof. The sealing tube 35 is engagedby a smooth piston 36, the end of which is rounded. The end portion 416of the sealing tube 35 is clamped by means of a clamp element 37 whichis secured to piston 36 by bolt 38. The cylindrical portion 37' of theclamp 37 is extended to form a piston guide portion for the piston 36.The clamp element 37 is formed with through-bores 39 which conduct theworking pressure fluid to the outside of the sealing tube 35. The otherend 418 of the sealing tube 35 merges into the transition zone A which,similar to the arrangement of FIG. 1, includes the partial elements 460,470, secured together at their junction surface 462. In the descriptionthat follows, similar parts have been given similar reference numerals,incremented by hundred numeral corresponding to the respective drawing.The transition zone A facing the sealing tube is formed with a thickenedportion 461 which, however, in contrast to the zone 61 of FIG. 1, islocated at the outside of sealing tube 35. The partial element 470 is,actually, a portion of the end 40 of the cylinder itself to which thetube 35 is engaged at the junction surface 462. In this embodiment aswell, the thickness of the partial element 460 decreases towards theoutside within the transition zone A so that, as in the embodiment ofFIG. 1, the localized stiffness and form stability of the transitionzone increase looked at from the side of the working pressure fluid.

A bore 43 in piston 36 provides working pressure fluid which can beapplied to the piston by a suitable connection screwed into the couplingbore of a coupling bolt 42. Bolt 42 also secures the holding end 44 tothe piston 36. The holding end 44 has threaded bores 45, 46 forconnection of pressurized lubricant supply and a bore 47 with a ringgroove 49 sealed by means of O-rings 50 located in grooves 48. Alongitudinal bore 51 communicates with groove 48 and conducts lubricantto the end 416 of tube 35. A small ring groove or gap 54 is formedbetween the head portion 53 and the piston 36 itself, sealed by anO-ring 52. The ring groove is similar to ring groove 19 (FIG. 3) topermit escape of the lubricant between the piston 36 and the sealingtube 35 and allow spreading of the lubricant and escape at the left endbeyond portion 418 of the tube 35 from between tube 35 and piston 36.The region beneath the tube 35 and, in transition zone A, forms ahydraulic choke of variable cross section controlled by the relativepressure of the working fluid and the lubricant. A sealing bellows 425is provided to collect lubricant leaking from and escaping from beneaththe left end of tube 35 for removal through duct 55.

The bolt 38 has a bore extending therethrough to permit working fluid toenter the cylinder chamber and to cause relative movement between thepiston and the cylinder. The working pressure fluid is applied to theoutside of the sealing tube 35 through the bores 39. The clamping bolt38 holds the clamp element 37 which, in turn, is secured to the end 416of the sealing tube 35 and further holds the head portion 53 to thepiston 36 itself. The cylinder chamber is closed off by an outer cover56 sealed by an O-ring 57. Lubrication is effected similar to thatexplained in connection with FIG. 1 and the same low coefficients offriction likewise here prevail.

The structure of FIG. 1 may require a larger passage 12 than that shownand described in connection therewith. If a larger duct is required, theend 516 of the sealing tube 417 (FIG. 5) can be constructed to have anexternally extending lip, as seen in FIG. 5. The other referencenumerals in FIG. 5 correspond to those of FIG. 1. The end portion 516 isheld in the wall of the bore 2 of the cylinder and by a preformed collarportion 3' of the bottom cover plate 503 of the cylinder for secure andsealed connection.

The transition zone A may have various shapes and arrangements withrespect to the partial elements thereof, as shown, for example, in FIGS.6 to 13.

FIG. 6: The transition zone A has two partial elements 660, 670 ofdifferent stiffness. The elements are attached or secured together forexample by adhesives, or by chemical bonding in a junction surface 662.The partial element 660 is an extension of the end 618 of the sealingtube which is formed with a thickened region 661. It has lesserstiffness than the partial element 670 which is connected at its portion666 to a piston (not shown).

FIG. 7: The transition zone A of the end 718 of the sealing tubeincludes three partial elements 760, 763, 770 having two junctionsurfaces 762, 762'. The junction surface between partial elements 760,763 extends at an inclination from the side of the working pressurefluid and passes through the surface of the transition zone A. Thepiston not shown is connected to the end portion 766 of partial element770.

FIG. 8 shows the end 818 of the tube in the transition zone A, and fourpartial elements 860, 864, 865, 870. The two partial elements 864, 865are formed as closed tubes or sleeves and are located between thepartial elements 860, 870. The relative stiffness of all the partialelements is different, decreasing in the direction towards partialelement 860 from the stiffest element 870. All junction surfaces 862 arewithin the transition zone A. End portion 866 of partial element 870 issecured to a piston not shown. The end 818 of the tube is formed with athickened region 861.

FIG. 9: The end 918 of the tube is located in a transition zone A formedof six partial elements. A thickened region 961 has a partial element960 of lowest stiffness applied thereto; four disk-shaped partialelements 965 of increasing stiffness are joined to the partial element960 and the last element 970 of highest stiffness is connected with itsend portion 966 to a piston not shown. The intermediate junctionsurfaces 962 include at least one secured bonded connection. Due to thelarger number of partial elements, with increasing stiffness, thepressure with respect to the support wall does not increase inexcessively great steps even if, as in this embodiment, the junctionsurfaces of the disk-shaped partial elements penetrate the surface ofthe transition zone A. Not all the junction surfaces have to be adheredtogether if the piston 966 is constantly loaded by a counteractingforce, for example by a spring, holding the elements together.

FIG. 10: The arrangement is similar to FIG. 9. The transition zone A hasseven partial elements. The partial element 1065 is joined to asleeve-like partial element 1063. The junction surfaces are shown at1062; the stiffest partial element 1070 is connected with its endportion 1066 to a piston not shown.

FIG. 11: The end 1118 of the sealing tube is within the transition zoneA and merges into partial element 1160 which has a decreasing thicknesslooked at from the side of the working pressure fluid. Five partialelements 1165 are located within the partial element 1160, as is thepartial element 1170 of highest stiffness which, again, is connectedwith its end portion 1166 to a piston not shown. A thickened portion ofend 1118 of the tube is shown at 1161. If the number of partial elementsof increasing stiffness is increased and the thickness of the partialelements is decreased then, in a limiting condition, a transition zonein which the stiffness changes continuously with respect to the lengthwill result. Such transition zone can be made of suitable plastic, forexample polyurethane, and can be so constructed that the piston may beregarded to form an integral part thereof.

FIG. 12: A corrugated metal tube 1217 is provided as axially deformablesealing member and has an end 1218 which is joined to the transitionzone A consisting of the partial elements 1267, 1268, 1270. Although thepartial elements may all consist of the same material, deformation ofthe transition zone is non-uniform. The partial element 1268 has a wallthickness which increases towards the piston. Preferably, the workingpressure fluid is applied from the inside against the partial element1268. The partial element 1268 forms a throttling region or choke forthe pressure lubrication flow and provides an automatically regulatedchoking passage therefor. Partial elements 1267, 1270 are provided forguidance. They may be formed with grooves at the outside thereof topermit passage of lubricant, as schematically shown at 1269, 1269'.

FIG. 13: The choke or throttle for the lubricant, in which the chokingor throttling action is controlled by the pressure of the workingpressure fluid, is located within the transition zone A. The transitionzone, joined to the end 1318 of the flexible tube, includes the partialelement 1360 with the thickening 1361 and a stiff, non-deformablepartial element 1370 merging into an end face 1366. The partial element1370 has a partial zone 1371 at the side of the sealing tube, which zone1371 is formed of reduced diameter relative to the adjacent zone 1372.The zone 1372 has a diameter which has just slight play with respect tothe wall of the cylinder.

The choke is formed by a piston 1376 which may be held by means of aspring 1374 against a stop or abutment 1375. A bore 1373 is incommunication with the working pressure fluid. The lubricant passesalong the zone 1371 and in the gap formed by the reduced diameterthereof and then through a passage 1377 toward the face of the piston1376 which is opposed to the face against which the working pressurefluid is applied. The lubricant forces the piston towards the left (FIG.13) and is relieved of pressure and drains off through drain line 1378which terminates in the ring duct selectively opened by leftwardmovement of the choke piston 1376. Thus a lubricant channel is formedbetween the lubricant flow passage and a low-pressure side, in whichchannel there is a regulating member of well defined shape and function.

A minor portion of the lubricant flows through the gap formed by theenlarged zone 1372 of the partial element 1370 and the inner wall of thecylinder. This gap may, if desired, be sealed, for example by an O-ring.The lubricant pressure is held in balance with the working fluidpressure also in the arrangement of FIG. 13. Movement of the chokepiston 1376 can be damped by suitable damping arrangements, not shown,and well known.

Partial elements in the form of thin metallic disks located betweenother partial elements of lower stiffness may be used. Also, partialelements of substantial stiffness which have surface coatings, orsurface layers of materials of lesser stiffness, can be used.

The transition zone A should be arranged to include partial elements ofdifferential stiffness and with junction surfaces passing through theoutside surface thereof. Such partial elements have steppedcharacteristics which are effective up to the outer surface of thetransition zone regarding localized deformation. Thus, the decrease ofpressure on the support wall occurs in steps within the transition zoneA or within a partial region thereof. Continuously decreasing pressureagainst the support wall can be obtained by a transition zone which haseither a continuously variable stiffness or a finite number of partialelements which are so arranged that the junction surfaces are locatedbeneath the surface of the transition zone and are continuous. The leaststiff (or most flexible) partial element then covers the entire surfaceof the transition zone, as shown in FIGS. 1, 4, 8 and 11, for example.Looked at from the working pressure fluid, the stability of shape of thetransition zone is progressively increasing.

The length of the transition zone A is indicated by the respectivearrows in the respective FIGURES, and extends from an end 18 (and 418,518 . . . 1318) of the sealing tube, that is, from that point at whichthe thickness of material of the sealing tube begins to vary, up to thepartial element which is connected to the piston (not shown). Theembodiments described in connection with FIGS. 6, 13 may be applied tothe arrangement shown in FIG. 4 or FIG. 5, and are not restricted to thespecific embodiment shown, which is illustrated in connection with thestructure specifically described in connection with FIG. 1.

The working pressure of the piston-cylinder combination may be high, forexample 100 at-gauge, and higher. The sealing tube 17, 35 may have goodcharacteristics regarding elasticity, due to its support on the wall ofthe cylinder, so that the force necessary to merely move the piston,that is, to overcome friction only, is low. The coefficient of frictioncan be so low that, when utilizing pressure lubrication, the coefficientof friction may be less than 0.001. This particularly low friction canbe obtained by the hydrostatic bearing obtained between the sealing tubeand the adjacent inner surface of the support wall, since the sealingtube surface and the inner surface of the support wall are not inphysical engagement with each other, due to the interposed film oflubricant.

If the working fluid is practically incompressible under high pressureoperating conditions the displacement of the piston-cylinder combinationis effectively directly proportional to the quantity of working pressurefluid supplied. The combination may be used for leakproof piston pumps,for servo positioning systems and the like. Placing two piston-cylindercombinations in paired arrangement and connecting the two pistons (orcylinders, respectively) together results in the double-actingcombination.

The pressure lubrication results in extremely low coefficients offriction. Low friction is also obtainable without pressure lubrication,however, if slippery sliding surfaces 21 are applied to the sealingtube, and/or to the engaging movable surface. Such sliding surface maybe elastic or flexible mesh or net systems made, for example, of smoothor textured manmade fibers or yarns, such as nylon, PTFE ("Teflon") orthe like. Threads, yarn, or woven or knit fabric made of such materialmay be applied to the sealing tubes, if necessary, with an intermediatelayer of other adhesive or adhering yarn or thread made, for example, ofelastic material, various types of elastomers, nylon, cotton, or thelike.

Various changes and modifications may be made and features described inconnection with any one of the embodiments may be used with any of theothers, within the scope of the inventive concept.

What I claim is:
 1. A piston and cylinder combination for high-pressurefluid applications, comprising:two working members movable relatively toeach other, one of said working members defining a piston and the otherthereof defining a cylinder; said working members defining therebetweena working chamber with strokes of increasing and decreasing workingchamber volume, said working chamber under operating conditions beingfilled with a working fluid under high pressure in at least a part ofone of said strokes; an at least partially cylindrical sealing memberconnected with each of said working members so as to seal the workingchamber, said sealing member being elastically deformable at least inits axial direction; a support surface provided at one surface of saidsealing member for supporting such sealing member against the highpressure of the working fluid in said working chamber; at the surface ofsaid sealing member facing said support surface there being provided alayer of a lubricant fluid streaming axially along said at leastpartially cylindrical sealing member and along said support surface froma lubricant inlet to a lubricant outlet; said deformable sealing memberhaving a transition zone defining a connection interface with one ofsaid working members which is arranged movable in relation to saidsupport surface, said connection interface of the transition zone ofsaid sealing member being chemically or physically bonded to saidmovable working member; said transition zone being arranged so as toform said lubricant fluid outlet and to allow the lubricant fluid toescape to a low-pressure region; and said transition zone further beingarranged so as to transmit a portion of said working fluid pressure tothe lubricant fluid and thereby to said support surface, saidtransmitted portion of the working fluid pressure decreasing downstreamwith the flow of lubricant fluid along the transition zone towards saidlubricant fluid outlet, the non-transmitted portion of the working fluidpressure being at least partially transferred via said connectioninterface to said movable working member.
 2. The apparatus as defined inclaim 1, wherein:said deformable sealing member in the region of saidtransition zone has a wall-thickness decreasing at least over part ofsaid transition zone in direction from said working chamber to saidlow-pressure side.
 3. The apparatus as defined in claims 2, wherein:saidtransition zone includes a portion of greater wall-thickness comparedwith the wall-thickness of said sealing member in the region of saidworking chamber; said portion of greater wall-thickness of saidtransition zone is located at the end of said transition zone near saidworking chamber.
 4. The apparatus as defined in claim 3, wherein:saidportion of greater wall-thickness of said transition zone is located atthe end of said transition zone near said working chamber.
 5. A pistonand cylinder combination for high-pressure fluid applications,comprising:two working members movable relatively to each other, one ofsaid working members defining a piston and the other thereof defining acylinder; said working members defining therebetween a working chamberwith strokes of increasing and decreasing working chamber volume, saidworking chamber under operating conditions being filled with a workingfluid under high pressure in at least a part of one of said strokes; anat least partially cylindrical sealing member connected with each ofsaid working members so as to seal the working chamber, said sealingmember being elastically deformable at least in its axial direction; asupport surface provided at one surface of said sealing member forsupporting such sealing member against the high pressure of the workingfluid in said working chamber; at the surface of said sealing memberfacing said support surface there being provided a layer of a lubricantfluid streaming axially along said at least partially cylindricalsealing member and along said support surface from a lubricant inlet toa lubricant outlet; said deformable sealing member having a transitionzone defining a connection interface with one of said working memberswhich is arranged movable in relation to said support surface, saidconnection interface of the transition zone of said sealing member beingchemically or physically bonded to said movable working member; saidtransition zone being arranged so as to form said lubricant fluid outletand to allow the lubricant fluid to escape to a low-pressure region; andthe shape of said sealing member in the region of said transition zonevarying in the direction from the working chamber to the lubricant fluidoutlet to a low-pressure region in such a manner that the pressureexerted by the sealing member under the action of the working fluidpressure via the lubricant fluid on the support surface decreases in thesaid direction.